In the motor vehicle field, a rotary electrical machine with excitation is known which is used as an alternator or alternator-starter, and comprises a rotary inductor which is provided with an excitation coil and a stator with a plurality of windings.
When the machine is operating as an alternator and the inductor is rotating, the stator windings provide alternating voltages which are rectified in order to obtain a direct voltage. This direct voltage is regulated such as to provide the on-board electrical supply network of the vehicle with a constant direct voltage for charging of the battery and supply to the consumers which are connected to the network.
The output voltage of the alternator is regulated conventionally by adjusting the excitation current which circulates in the inductor coil.
For a constant speed of rotation and charge, the response of the alternator to a variation of the excitation current is limited by the intrinsic pass-band of the system, which depends on the electromechanical characteristics of the alternator.
For motor vehicle applications, the output voltage must be regulated such as to remain constant in operating ranges (ranges of speed of rotation and electrical charge represented by the battery and the consumers) which are defined by the vehicle manufacturers.
For this purpose, in a motor vehicle alternator, the output voltage is measured and compared continually with a set value by a regulator device which controls the excitation current such as to minimise or eliminate the error between the output voltage measured and the set value.
The company VALEO EQUIPEMENTS ELECTRIQUES MOTEUR has already proposed to carry out this regulation on the basis of measurements by sampling, by means of digital techniques which provide substantial advantages in comparison with the conventional analogue methods, and in particular in its European patents EP 0 481 862 and EP 0 802 606.
However, implementation of the digital processing algorithms on microcontrollers does not make it possible to modify easily the gain and/or the pass-band and/or the stability and/or the reference input of the regulator loop.
In addition, these algorithms must carry out calculations on a large number of bits, which leads to the use of analogue-digital converters which have a high resolution and are consequently costly.
Finally, the diversity of the algorithms, which are adapted to each particular application, does not permit standardisation which would make their intellectual property rights easier to protect.
Consequently, there is a need for a rotary electrical machine with excitation, provided with a digital regulator which eliminates the disadvantages of the digital regulators known in the prior art.